Thermal management system

ABSTRACT

A thermal management system for a body to be exposed to solar radiation includes an infrared radiating element and a solar-scattering cover disposed on or integrated with the infrared radiating element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Ser.No. 62/845,017, filed May 8, 2019, the contents of which is incorporatedby reference herein in its entirety.

BACKGROUND

Radiative cooling may alleviate urban heat island effects and decreasethe energy requirements for building thermal regulation. Nevertheless,existing radiative cooling systems may be considered unsuitable forclimates with low atmospheric clarity and high humidity levels.

New utility-scale solar photovoltaic (PV) installations are deployingtracking and bifacial-cell technologies because they improve efficiency,and in turn, decrease costs. The potential gain in efficiency is partlyoffset, however, by the higher operating temperatures associated withhigher illumination levels. Higher operating temperatures may degradeboth PV module efficiency (˜0.4%/° C.) and module lifetime (˜7%/° C.).

A passive approach to reduce the module operating temperature is todirectly reject heat to Space, effectively at ˜3 K. However, existingon-module radiative cooling approaches have not demonstrated more than1° C. of additional temperature drop relative to a conventionalglass-covered module.

INTRODUCTION

In a first aspect, a thermal management system for a body to be exposedto solar radiation comprises: an infrared radiating element; and asolar-scattering cover disposed on or integrated with the infraredradiating element.

In some examples of this first aspect, the solar-scattering cover is toscatter sunlight diffusely or directionally away from the body; thesolar-scattering cover is substantially transparent to infraredradiation; and the infrared radiating element is to emit infraredradiation through the solar-scattering cover. In some examples, thesolar-scattering cover comprises a nanostructured, IR-transparentpolymer. In some examples, the nanostructured, IR-transparent polymer isnanostructured polyacrylonitrile (nanoPAN). In some examples, thesolar-scattering cover includes a film, the film comprising thenanostructured, IR-transparent polymer. In some examples, the filmcomprises: a first layer including a first flexible polymeric material;a second layer disposed on the first layer, the second layer includingthe nanostructured, IR-transparent polymer; and a third layer disposedon the second layer, the third layer including a second flexiblepolymeric material, wherein the film is to be removably installed on theinfrared radiating element. In some examples, the film is further to bereinstalled on the infrared radiating element after being removed fromthe infrared radiating element. In some examples, the nanostructured,IR-transparent polymer includes nanostructured polyacrylonitrile(nanoPAN). In some examples, the first flexible polymeric materialincludes polyethylene. In some examples, the second flexible polymericmaterial includes polyethylene. In some examples, the thermal managementsystem further comprises a dielectric material disposed on or embeddedin the nanostructured, IR-transparent polymer to increase solarscattering of the solar-scattering cover and to protect thenanostructured, IR-transparent polymer from ultra-violet radiation.

It is to be understood that any features of the thermal managementsystem disclosed herein may be combined together in any desirable mannerand/or configuration.

In a second aspect, a film to be disposed on an infrared radiatingelement, the film comprises: a first layer including a first flexiblepolymeric material; a second layer disposed on the first layer, thesecond layer including a selectively transparent polymeric material; anda third layer disposed on the second layer, the third layer including asecond flexible polymeric material, wherein the film is to be removablyinstalled on the infrared radiating element.

In some examples of this second aspect, the film is further to bereinstalled on the infrared radiating element after being removed fromthe infrared radiating element. In some examples, the selectivelytransparent polymeric material includes nanostructured polyacrylonitrile(nanoPAN). In some examples, the first flexible polymeric materialincludes polyethylene. In some examples, the second flexible polymericmaterial includes polyethylene.

It is to be understood that any features of the film disclosed hereinmay be combined together in any desirable manner and/or configuration.Further, it is to be understood that any combination of features of anyaspects of the thermal management system and/or the film disclosedherein may be used and/or combined together in any desirable manner,and/or may be used and/or combined with any of the examples disclosedherein.

In a third aspect, a thermal management system for a photovoltaic (PV)power generator comprises: an infrared radiating element; asolar-scattering cover disposed on the infrared radiating element; and athermal storage sub-system in fluid connection with a solar panel viathermal interconnections.

In some examples of the third aspect, the solar-scattering cover is toscatter sunlight diffusely or directionally toward an underside of thesolar panel; and the solar-scattering cover is substantially transparentto infrared radiation to allow the infrared radiating element to emitinfrared radiation through the solar-scattering cover. In some examples,the solar-scattering cover comprises a nanostructured, IR-transparentpolymer. In some examples, the nanostructured, IR-transparent polymer isnanostructured polyethylene (nanoPE). In some examples, thenanostructured, IR-transparent polymer is nanostructuredpolyacrylonitrile (nanoPAN). In some examples, the thermal managementsystem further comprises a dielectric material disposed on or embeddedin the nanostructured, IR-transparent polymer to increase solarscattering of the solar-scattering cover and to protect thenanostructured, IR-transparent polymer from ultra-violet radiation. Insome examples, the dielectric material is deposited on thenanostructured, IR-transparent polymer by physical vapor deposition orby a solution-based process, or embedded into the nanostructured,IR-transparent polymer by electrospinning. In some examples, the thermalstorage sub-system is to shift and distribute a peak solar heat loadover a twenty-four hour time period; the thermal storage sub-system isto store excess off-peak cooling for use during peak hours; the thermalstorage sub-system is to store natural convection energy; and thethermal storage sub-system comprises a container to store a coolant. Insome examples, the container is located under the infrared radiatingelement or the container is thermally connected to the infraredradiating element via the thermal interconnections. In some examples,the container is connected to the solar panel with a circulating coolantline or with heat pipes, wherein the heat pipes are stationary orwherein the heat pipes are to oscillate. In some examples, the thermalinterconnections comprise a circulating fluid loop or a heat pipe. Insome examples, the thermal interconnections are passive. In someexamples, the dielectric material is selected from the group consistingof ZnS, ZnO, TiO2 and combinations thereof.

In some examples of the third aspect, the solar panel is a member of anarray of tracking solar panels arranged in rows; the infrared radiatingelement is a solar-scattering radiator located between the rows of thearray of tracking solar panels; a radiating area of the solar-scatteringradiator is about equal to an area of the solar panel; thesolar-scattering radiator is to work in tandem with natural convectionfrom the array of tracking solar panels; and the thermal storagesub-system includes a ground-based liquid reservoir. In some examples,the thermal management system further comprises: a sun-facing surfacedefined on at least one member of the array of tracking solar panels; adistal surface defined on the at least one member of the array oftracking solar panels opposite the sun-facing surface; and a heatexchanger attached to the distal surface of the at least one member ofthe array of tracking solar panels. In some examples, the heat exchangerincludes a serpentine tube; and the heat exchanger is to obscure lessthan 20 percent of the distal surface of the solar panel to which theheat exchanger is attached. In some examples, the array of trackingsolar panels includes at least one bifacial solar panel. In someexamples, the thermal interconnections include flexible tubing tofluidly connect the ground-based liquid reservoir to the serpentinetube, wherein the flexible tubing remains connected to the serpentinetube throughout a range of motion of a tracking solar panel in the arrayof tracking solar panels to which the serpentine tube is attached.

In some examples of the third aspect, the ground-based liquid reservoiris covered by the solar-scattering radiator. In some examples, thesolar-scattering radiator includes: a layer of mirrored aluminum; acoating disposed on the layer of mirrored aluminum, the coating toabsorb or emit radiation having wavelengths ranging from mid-wavelengthinfrared to long-wavelength infrared; and a solar scattering coveroverlaid on the coating, wherein the solar scattering cover issubstantially transparent to infrared radiation to allow thesolar-scattering radiator to emit infrared radiation through thesolar-scattering cover. In some examples, the coating is a selected fromthe group consisting of: polydimethylsiloxane (PDMS) or an otherpolymer; an inorganic material; and combinations thereof. In someexamples, the coating is polydimethylsiloxane (PDMS). In some examples,the solar-scattering cover comprises a nanostructured, IR-transparentpolymer. In some examples, the nanostructured, IR-transparent polymer isnanostructured polyethylene (nanoPE). In some examples, thenanostructured, IR-transparent polymer is nanostructuredpolyacrylonitrile (nanoPAN). In some examples, the thermal managementsystem further comprises a dielectric material disposed on or embeddedin the nanostructured, IR-transparent polymer to increase solarscattering of the solar-scattering cover and to protect thenanostructured, IR-transparent polymer from ultra-violet radiation. Insome examples, the dielectric material is deposited on thenanostructured, IR-transparent polymer by physical vapor deposition orby a solution-based process, or embedded in to the nanostructured,IR-transparent polymer by electrospinning. In some examples, thedielectric material is selected from the group consisting of ZnS, ZnO,TiO2 and combinations thereof.

It is to be understood that any features of the thermal managementsystem disclosed herein may be combined together in any desirable mannerand/or configuration. Further, it is to be understood that anycombination of features of any aspects of the thermal management systemand/or the film disclosed herein may be used and/or combined together inany desirable manner, and/or may be used and/or combined with any of theexamples disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of examples of the claimed subject matter willbecome apparent by reference to the following detailed description anddrawings, in which like reference numerals correspond to similar, thoughperhaps not identical, components. For the sake of brevity, referencenumerals or features having a previously described function may or maynot be described in connection with other drawings in which they appear.

FIG. 1 is a schematic illustration depicting an example of aRadiation-Assisted PV Thermal management system according to the presentdisclosure;

FIG. 2 is a schematic cross-sectional view of an example of a radiativecooler with a solar-scattering infrared-transparent nanostructured coveraccording to the present disclosure;

FIG. 3 is a schematic cross-sectional view of another example of aradiative cooler with a solar-scattering infrared-transparentnanostructured cover according to the present disclosure;

FIG. 4 is a schematic cross-sectional view of an example of a radiativecooler with a removable selectively transparent film according to thepresent disclosure;

FIG. 5 is a photograph and infrared image of a solar-scatteringinfrared-transparent nanostructured cover depicted in FIG. 4 showingvisible opacity on the left and infrared transparency on the right; and

FIG. 6 is a graph depicting reflectance spectra for the samples listedin Table 1 as disclosed herein.

DETAILED DESCRIPTION

Disclosed herein is a selectively transparent film includingpolyacrylonitrile (PAN) nanofibers that can be seasonally deployed overexisting surfaces to enable radiative cooling during the summer, whileallowing solar heating when removed during the winter. As disclosedherein, the morphology of the PAN nanofibers is tailored to exhibit highsolar cross-sections. Such morphology decreases the amount of materialneeded and, in turn, causes the film to exhibit high infraredtransmittance despite PAN's intrinsic absorption in the 8-13 μm range.As disclosed herein, beaded nanofiber electrospun film boosts the totalsolar reflectance on an unpolished aluminum surface from ˜80% to nearly99%. When scaled up and tested outdoors, the film shields a PDMS-coatedaluminum sheet from solar radiation while allowing the PDMS-coatedaluminum sheet to radiate heat to space, resulting in a 7° C.temperature drop under unoptimized sky conditions. Heat transfermodeling agrees with the outdoor experiments and predicts temperaturedrops exceeding 10° C. below ambient under standard sky conditions withthe beaded nanofiber film. The flexible and freestanding nature of thefilm may allow it to be deployed seasonally in regions where it isfavorable to reflect sunlight during warmer months but absorb solar heatduring colder months. This would widen the geographical space whereradiative cooling is applicable.

Passive radiative cooling is one approach that has the potential toalleviate urban heat island effects and decrease the energy consumed forbuilding thermal regulation. This approach takes advantage of theatmospheric transparency windows in the infrared (3.4 μm-4.1 μm, 8 μm-13μm, and 16 μm-28 μm) to allow terrestrial materials to radiate heat toSpace (˜3 K). As used herein, selectivity with respect to a radiatormeans the radiator can emit heat to Space while preventing absorption ofsolar irradiation. As used herein, “mid-wavelength infrared” refers toelectromagnetic radiation having a wavelength from about 3 μm to about 8μm. As used herein, “long-wavelength infrared” refers to electromagneticradiation having a wavelength from about 8 μm to about 15 μm.

Before the present disclosure, radiative cooling approaches were bestsuited for climates with high atmospheric clarity and low humiditylevels. In seasonal climates, a thermal management system, as disclosedherein, with two operational modes, would use less energy. In a firstoperational mode, the thermal management system radiatively cools duringthe summer. In a second operational mode, the thermal management systemabsorbs sunlight during the winter. The bimodal approach of the presentdisclosure could offset cooling and heating demands that are otherwisemet using renewable electricity or fossil fuels.

According to the present disclosure, a selectively transparent film canbe seasonally deployed over existing materials to lower theirtemperatures. A freestanding, selectively transparent film is aversatile device that can be placed in contact with anemitting/radiating surface or separated from the emitting/radiatingsurface by a transparent insulation layer. In examples, the film mayinclude electrospun polyacrylonitrile (PAN) fibers, supported by thinpolyethylene (PE) sheets. By tailoring the hierarchical morphology ofthe PAN structures, examples of the freestanding PAN-based film of thepresent disclosure may achieve greater than 95% solar-weighted totalreflectance (SR) and greater than 70% atmospheric-window-weighted totaltransmittance (AWT). As such, the selectively transparent film can bepaired with emitting/radiating surfaces that have relatively low solarreflectance. It is to be understood that many materials used in urbansettings (e.g., concrete, asphalt, roofs, etc.) have relatively lowreflectance. During warmer months, examples of the PAN film of thepresent disclosure can be deployed to provide passive radiative cooling.During colder months, when a solar-absorbing surface is favorable, thePAN film of the present disclosure can be easily removed and stored forlater use.

In addition to being seasonally versatile, examples of the film of thepresent disclosure can provide optimized cooling regardless of thecooling power demand. When placed directly on the emitter/radiator,radiation can augment natural thermal regulation mechanisms such asconduction and convection to the environment. As disclosed herein, athermal management system 20 having a combined operational mode, withconduction, convection, and radiation aspects, is useful for thermalmanagement in applications where heat dissipation exceeds the radiativecooling power (e.g. solar panels). In low power applications, wheresub-ambient temperatures are possible, a thermal break between theemitter/radiator and the environment can enable higher performance. Inthis scenario, the film 35 of the present disclosure can be astand-alone cover or be paired in tandem with an IR-transparentinsulator to decrease heat transfer between the emitter/radiator andwarmer environment. The seasonal versatility and cooling powerversatility of examples of the present disclosure provide enhancedutility in a wider range of climates.

Referring to FIG. 2, in an example, a thermal management system 20 for abody 17 to be exposed to solar radiation 19, includes an infraredradiating element 22 and a solar-scattering cover 24 disposed on theinfrared radiating element 22. In some examples, the solar-scatteringelement can be integrated with the infrared radiating element. It is tobe understood that emission may occur partly from the solar-scatteringelement and partly from the infrared radiating element, therebyincreasing cooling power. As used herein, a “body” means any structure.By way of non-limiting example, a body may include: a building, a roof,a wall, a window, a door, a hatch, a boat, an automobile, an airplane, alighter-than-air vehicle; a machine, a housing, an electronic device, asolar panel, a container, a greenhouse, a swimming pool, a waterreservoir, or combinations thereof.

In some examples of the thermal management system 20, thesolar-scattering cover 24 may be to scatter sunlight 11 diffusely ordirectionally away from the body 17. The solar-scattering cover 24 maybe substantially transparent to infrared radiation 26. As used herein,substantially transparent to infrared radiation means that at least 75percent of the infrared spectrum passes through the solar-scatteringcover 24 with less than a 25 percent attenuation of intensity. Theinfrared radiating element 22 may be to emit infrared radiation 26through the solar-scattering cover 24.

In some examples, the solar-scattering cover 24 comprises ananostructured, IR-transparent polymer 21. In some examples, thenanostructured, IR-transparent polymer 21 is nanostructuredpolyacrylonitrile (nanoPAN) 29 (FIG. 3).

Referring to FIG. 4, in some examples, the solar-scattering cover 24includes a film 35; the film 35 includes the nanostructured,IR-transparent polymer 21. In some examples, the film 35 includes afirst layer 36, a second layer 37, and a third layer 38. The first layer36 may include a first flexible polymeric material 41. The second layer37 may be disposed on the first layer 36. The second layer 37 mayinclude the nanostructured, IR-transparent polymer 21. The third layer38 may be disposed on the second layer 37. The third layer 38 mayinclude a second flexible polymeric material 42. In an example, the film35 is to be removably installed on the infrared radiating element 22. Insome examples, the film 35 is further to be reinstalled on the infraredradiating element 22 after being removed from the infrared radiatingelement 22. In some examples, the nanostructured, IR-transparent polymer21 includes nanostructured polyacrylonitrile (nanoPAN) 29. In someexamples, the first flexible polymeric material 41 includespolyethylene. In some examples, the second flexible polymeric material42 includes polyethylene. In examples, the first layer 36 may be a PEsheet 18. In some examples, the third layer 38 may also be a PE sheet18. The first layer 36 and the third layer 38 may include the samematerials, or they may include different materials. The first layer 36and the third layer 38 may have the same thickness, or they may havedifferent thicknesses. In some examples, the thermal management system20 further includes a dielectric material disposed on or embedded in thenanostructured, IR-transparent polymer 21 to increase solar scatteringof the solar-scattering cover 24 and to protect the nanostructured,IR-transparent polymer 21 from ultra-violet radiation.

FIG. 5 is a photograph and infrared image of a solar-scatteringinfrared-transparent nanostructured cover depicted in FIG. 4 showingvisible opacity on the left and infrared transparency on the right. ABlock M was covered on the left side of the Block M by asolar-scattering cover 24 (see FIG. 4). The solar-scattering cover 24(FIG. 4) includes the film 35 (FIG. 4). The film 35 includes nanoPAN 29.The left side of FIG. 5 is a visible light photograph. The right side ofFIG. 5 is an infrared image. FIG. 5 demonstrates that the nanoPAN isopaque to visible light, and substantially transparent to infraredlight.

As disclosed herein, fiber morphology affects the scattering andabsorption properties of the selectively transparent films. The fibermorphology may be modified by varying the polymer concentration in theelectrospinning solution. As disclosed herein, scattering mechanismswere unexpectedly and fortuitously discovered by experimental studiescombined with electromagnetic simulations.

To further illustrate the present disclosure, an example is givenherein. It is to be understood that this example is provided forillustrative purposes and is not to be construed as limiting the scopeof the present disclosure.

Example

To demonstrate the versatility of present disclosure, the selectivelytransparent cover is combined with an unpolished aluminum sheet. Foroutdoor testing, the aluminum sheet is coated with polydimethylsiloxane(PDMS) to increase its thermal emittance. Without the nanoPAN film, theunpolished aluminum sheet has ˜80% SR. With the PAN film, the SRincreases to nearly 99%.

The morphology of polymer fibers may be controlled by tuning variousspinning parameters in an electrospinning process. Voltage, polymerconcentration, spin time, stage height, flowrate, and syringe gauge areall parameters that can affect the resulting electrospun fiber. In anexample, the polymer solution concentration and spin time may be variedwhile keeping all other variables constant. The polymer solutionconcentration and spin time may be the simplest to tune to change fibermorphology and film thickness. PAN concentration directly influences thesolution viscosity which influences the morphology of the spun fibers.Spin time influences the mass deposited, which in turn, affects theoptical thickness. Ideally, the film needs to be thick enough toattenuate solar rays before they reach the emitter, but thin enough tobe transparent in the infrared and enable heat exchange with Space.

In some examples, high-purity polyethylene (PE) may be used as aconvection cover for passive radiative cooling. The simple chemistry ofPE (C2H4)n means that absorption peaks only occur for C—H and C—C bonds,resulting in high transmission in the infrared. PAN is more absorptivein the IR than polyethylene due to its extra triple nitrogen bond(C3H3N)n and has never been reported as being used as a passiveradiative cooling cover. Nonetheless, PAN was fortuitously chosen. PANis compatible with electrospinning, unlike PE which requires additionalheating and solvent treatment to enhance its electrostatic properties.By tailoring the morphology using electrospinning, a decrease in theamount of material needed to achieve high SR while retaining high AWTwas discovered.

Four different concentrations of PAN dissolved in dimethylformamide(DMF) were prepared and electrospun onto transparent PE films: 2.5 wt %,5 wt %, 7 wt %, 9 wt %. The resulting nanoPAN films were qualitativelyopaque in the visible region but transparent in the IR. These areadvantageous traits to scatter solar radiation but allow emission in theatmospheric windows. The 2.5 wt % and 5 wt % concentrations bothresulted in a beaded fiber morphology, while the 7 wt % and 9 wt %concentrations produced cylindrical fibers. For low concentrations andviscosities, high surface tension causes instabilities in Taylor coneformation resulting in droplets and bead formation. When theconcentration is increased, viscous forces dominate resulting in moreuniform cylindrical fibers.

To protect the nanoPAN films and prevent the nanoPAN from sticking whilehandling, the nanoPAN may be sandwiched between two transparent PEsheets. The resulting freestanding film can either be used as aconvective cover or applied directly on the emitter depending on thecooling application. In both applications the transparency of the fiberfilms in the infrared enables the heat exchange with Space. The AWTdecreases with increasing concentrations of PAN. This effect may beattributed to the increase in area density (i.e., mass per area) of PANwith increasing concentration (electrospinning time is held constant).The increase in area density may lead to a decrease in infraredtransparency, consistent with the Beer-Lambert law. This effect is alsocorroborated by the AWT results with increasing fiber thickness for afixed PAN concentration.

In addition to the infrared properties, solar reflectance of the PANfilm enhances daytime radiative cooling and seasonal thermal management.UV-Vis measurements show that a beaded 5 wt % PAN fiber (freestandingfilm) has a solar reflectance of 95%, which is the highest across thesamples in the present disclosure, despite the intermediate areadensity. The infrared and solar specular measurements for the 5 wt %PAN, 720 μm thick film matches both the atmospheric transparency andsolar irradiance spectrum. Although the beaded 5 wt % PAN film hadnearly the same area density as a cylindrical 7 wt % film, its SR andAWT values were substantially higher.

To demonstrate why the beaded fiber morphology exhibits higher solarreflectance, SCUFF-EM simulation was used to compare the electromagneticresponse of this composite structure to its constituent structures(bead, cylinder). The beaded morphology results in a higher scatteringcross-section compared to a uniform cylindrical fiber. The dielectricnanostructures exhibit scattering resonances when their size iscomparable to the wavelength of light, consistent with Mie theory.Increasing the diameter leads to a red shift of the scattering peak forcylinders. In the case of a beaded morphology, the resultingcross-section can be largely explained by a sum of the individualcross-sections of the bead and cylinder. It is to be understood,however, that the combination of structures and length scales in thebeaded fiber morphology results in a higher solar-weighted scatteringefficiency than either the fiber or bead alone. This may be due to thesmaller geometrical cross-section of the beaded fiber than the sum ofthe constituent structures (due to overlapping volumes in the beadedfiber). The cylindrical fibers scatter shorter wavelengths due to theirthinner diameters, while the beads primarily scatter in the near-IR dueto their larger characteristic length scale. Thus, electrospinningprovides a means to include cylindrical and bead morphologies in amechanically interconnected system and take advantage of both dielectricmicro/nanostructures.

In addition to morphological effects, polydispersity can also beresponsible for broadening the overall solar reflectance. Both the 7 wt% (cylinder) and 5 wt % (beaded) films feature relatively broaderparticle size distributions compared to the 9 wt % (thicker cylinder)and 2.5 wt % samples (thinner beaded). However, the 5 wt % beadedmorphology exhibits notably higher SR than the 7 wt % cylindricalgeometry, suggesting that polydispersity cannot entirely explain thedifference in SR.

Outdoor Tests

Outdoor tests were conducted to validate heat transfer models and totest whether the nanoPAN-based configurations can outperformconventional roofing materials and existing commercial films underrealistic sky conditions. Based on the UV-Vis and Fourier TransformInfrared (FTIR) results, discussed above, the beaded morphology (5 wt %PAN) was chosen as the best candidate for daytime cooling. An unpolishedaluminum sheet (Al) was chosen as a conventional roofing surface that isunoptimized for radiative cooling. The stagnation temperature of threeemitter systems (Table 1) was simultaneously monitored under clear skyconditions in Ann Arbor, Mich.

TABLE 1 Description of emitter-cover systems tested outdoors System I IIIII label unpolished Al with nanoPAN ESR control Emitter PDMS-coatedbeaded PAN nanofibers ESR film adhered unpolished deposited onto to analuminum aluminum Al-PDMS emitter sheet

FIG. 6 is a graph depicting reflectance spectra for the samples listedin Table 1 above. FIG. 6 depicts total reflectance of the ˜6 cm²emitters fabricated using electrospinning. These results were used inthe “standard clear sky” heat transfer model of cooling power versusemitter temperature for the (I) unpolished Al, (II) with nanoPAN, and(III) ESR control samples listed in Table 1. FIG. 6 shows that sample II(with nanoPAN) had the highest SR, and sample I (unpolished Al) had thelowest SR.

Outdoor Test Results

The outdoor test results show that the unpolished aluminum (sample I)exhibited the highest temperature (20.1° C.) due to its low solarreflective properties (SR=80%). In contrast, the coldest averagetemperature was achieved with the “with nanoPAN” configuration(II)system which also resulted in lower absolute temperatures than theEnhanced Specular Reflector (ESR) control (sample III). Furthermore, byshielding the unpolished aluminum with the nanoPAN film, a ˜7° C.temperature drop was observed because of the high SR of the nanoPANfilm. Further, placing the nanoPAN film over a calibrated blackbodysurface under AM1.5G 1-sun irradiation resulted in a 38.5° C. reductionin stagnation temperature.

The outdoor stagnation temperature measurements agree with thesemi-empirical heat transfer model. Inputs to the heat transfer modelinclude measured optical properties of the covers and emitters (forexample, see FIG. 6), measured thermal insulation of the housing (i.e.,thermal resistance between the emitter and the surroundings), ambienttemperature, and the solar orientation. Small differences between themodel and the experimental stagnation temperatures can be attributed tohumidity and cloud coverage, which are not explicitly taken into accountin the model.

It is to be understood that these results should not be interpreted asthe best possible cooling performance that the present disclosure canachieve because during scale up from 5.9 cm² samples, which had ˜99% SR,to wafer-scale covers (38.5 cm²) used for outdoor measurements, adecrease in SR due to non-uniform deposition was observed. Furthermore,the average ambient temperature during the reporting window was 14° C.,which suppresses the radiative cooling power relative to conditions withwarmer ambient temperatures. Nevertheless, the results demonstrate thatthe addition of scattering fibers, albeit unoptimized, onto anunpolished surface resulted in better performance than the highlyreflective ESR control.

Fabrication of Polymer Films

PAN fibers were fabricated using a home-built electrospinning setup. PANpowder with a MW of 200,000 (Polysciences, Inc.), was dissolved indimethylformamide (Sigma) for a 2.5, 5, 7, and 9 wt % concentrations andmixed at 40° C.-50° C. overnight or until the powder was fullydissolved. Below 2.5 wt %, the solution was not viscous enough tosupport fiber formation, while above 9 wt %, the solution was tooviscous. The solution was loaded into a syringe with a 25-gauge blunttip needle and placed in a syringe pump to ensure a constant flowrate.The PAN solution was electrospun at a flow rate of 0.4 mL/hr and stageheight of 11.5 cm for 10, 20, 40, and 60 minutes. The voltage wasadjusted for each concentration to ensure formation of a Taylor cone.The substrates consisted of PDMS on aluminum emitter and PE plastic wrapplaced over aluminum for grounding. Post fabrication treatment includedleaving the films to rest overnight and carefully placing a clean PEplastic wrap on top of the exposed PAN fibers as a protective layer.

Fabrication of PDMS Emitters

The sides of aluminum weigh boats were removed and used as substratesfor the unpolished aluminum surfaces. A 10:1 base elastomer to curingagent was used to make the pre-cured PDMS mixture. A 100 μm layer ofPDMS was deposited on the aluminum substrate by spin coating at 700 rpmfor 30 seconds and curing at 80° C. for 24 hours. Commercially available3M Vikuiti™ ESR reflective emitters were purchased and placed over analuminum substrate as a control.

Optical Measurements and Microscopy

The optical properties of the film were measured using UV-Vis and FTIRspectrometers with integrating sphere attachments. Total reflectance wasmeasured from 0.3-1.2 μm using a Shimadzu UV-3600 Plus UV-Vis. Totalinfrared transmittance and reflectance was measured from 2-18 μm using aCary 670 benchtop FTIR. Optical measurements were taken for bothfree-standing PAN fibers and emitters. Fiber morphology was visualizedusing the TESCAN MIRA3 scanning electron microscope. Bead and fiberdiameter distributions were analyzed using the TESCAN images.

Scuff-EM Model

The scattering cross-sections of the cylindrical and beaded fibermorphologies were computed numerically with an open-source softwareimplementation of the boundary-element method (BEM). Mesh-refinement wascompleted to ensure accurate results at smaller wavelengths. The BEM wasverified by comparing the results to an analytical solution for Miescattering via a PAN microsphere.

Outdoor Measurements

Outdoor tests were taken over 24-hour periods in Ann Arbor, Mich. whenthere was minimal cloud coverage. The emitter temperature, ambienttemperature, and humidity were logged as a function of time for theemitter samples and a 3M ESR emitter control. Emitter temperatures weremeasured using T-type thermocouples and Extech SDL200 datalogger whiletransient ambient temperatures and humidity were logged using an OMEGAOM-24 logger. The emitters were placed in a foam enclosure to preventbottom and side heating and the outside of the foam enclosure waswrapped with reflective Mylar®. An infrared transparent cover consistingof polyethylene (Glad® Cling Wrap) was placed taut over the emitter as aconvective cover.

Examples of the thermal management system of the present disclosure maybe combined with solar panels (i.e. photovoltaic (PV) modules). ARadiation-Assisted PV Thermal (RAPT) management system is disclosedherein.

Examples of the RAPT system disclosed herein may help regulate PV moduletemperature while enhancing back-side illumination levels for bifacialPV modules. Examples of the RAPT system disclosed herein maycontinuously maintain solar modules/panels at 7.5 (+/−15)° C. above theaverage daytime ambient temperature. According to the presentdisclosure, the RAPT system accomplishes this by (i) disposing asolar-scattering radiator as disclosed herein between the rows oftracking solar arrays (equal in the area as the arrays) and (ii)advantageously applying stored nighttime radiative cooling/convectionusing a liquid reservoir. The radiator provides an average cooling rateof about 120 W/m² by emitting heat through the atmosphere's infrared(IR) transparency bands. The radiator works in tandem with naturalconvection from the above-ambient PV modules, which provides anadditional average cooling rate of about 160 W/m². Assumptions for thiscalculation are shown in Table 2:

TABLE 2 Assumptions for calculations Temperatures: proposedradiator/reservoir/panels: 32.5 +/− 2.5° C.; average daytime ambient:25° C.; average nighttime ambient: 18° C.; current panel(power-output-weighted): 49° C. Radiator: 80% radiator capacity factor(daytime and nighttime); radiating area matches panel area. Liquid loopand reservoir: pressure drop calculated based on 8 m pipe length per 1m² of panels (¼ in. diameter); coolant: glycol-water mixture; 5 cmreservoir depth; reservoir: aluminum container; 85% liquid pumpefficiency Natural convection: heat transfer coefficient (20 W/m²K) isbased on empirical data for on-sun temperature rise (~25 C.) and on-sunheat dissipation rates (~500 W/m²) of representative panels. Solarpanels/farms: 15% average solar reflectance; 20% power conversionefficiency at room temperature (projecting to 2025); 50% panel areacoverage; 30% solar capacity factor; all-in installation costs$0.7/W_(e) (projecting to 2025).

Together, these two nearly continuous modes of heat transfer exceed theon-sun heat gain by the solar panels as long as excess nighttime coolingenergy is stored in the liquid reservoir and circulated during the day.The pumped coolant heat exchanges with the panels using a rear-mountedserpentine tube (covering <6% of the panel area for compatibility withbifacial cells). Flexible tubing connects the reservoir to therear-mounted coolant lines and allows the panels to track freely. Thepower consumed for circulating the coolant is less than about 5% of thepanel output power.

In an example, the RAPT system is applied for PV system cooling. TheRAPT system may decrease average module temperatures by 15-20° C.(power-output weighted) and buffer temperature swings. The decreasedaverage module temperatures may translate into a 6-8% increase in modulepower output and efficiency (based on the crystalline Si temperaturecoefficient). Based on the temperature drop, RAPT may also improve PVmodule reliability and extended lifetimes that surpass Department ofEnergy (DOE) targets (>30 years).

A Levelized Cost of Energy (LCOE) analysis was performed to determinethe allowable additional cost for the RAPT system while maintaining abaseline LCOE of 0.056 $/kWh (25 yr baseline lifetime). The LCOEanalysis applied an LCOE calculator developed by the National RenewableEnergy Laboratory (NREL) and a market overview organized by NREL toestablish the baseline cost for a photovoltaic Megawatt (MW) facility.The estimated 7.2% efficiency gain and prolonged lifetime (30 years) areworth over $50/m² (or ˜25 cents/Watt) even when accounting for higheroperation and maintenance costs ($2.00/kW/year increase).

The projected cost of goods for the RAPT system disclosed herein isabout 3-5 US Dollars ($)/m². The projected cost of goods allows for asufficient budget for installation and maintenance if those tasks arecoordinated/integrated with the overall solar farm. Further economicbenefits are expected for next-generation high-efficiency PV modules.Bifacial solar modules can particularly benefit from RAPT system asdisclosed herein by leveraging scattered sunlight by the cover for anadditional 5-10% relative increase in efficiency. Furthermore, panelthermal stability may also facilitate the commercialization of emergingPV technologies, such as tandems and perovskites, which are expected tobe more susceptible to temperature swings.

In some examples, the RAPT system of the present disclosure may beimplemented in off-the-grid applications requiring cooling such asatmospheric dew harvesting, cold storage, etc.

In some examples, the RAPT system of the present disclosure may beimplemented in passive cooling of roofs for thermal management and airconditioning of buildings.

In some examples, the RAPT system of the present disclosure may beimplemented in energy efficient cooling of wireless infrastructure.

The inventors of the present disclosure have unexpectedly andfortuitously discovered the solar-scattering radiator and the integratedcooling storage of the RAPT system as disclosed herein. Some existingradiative cooling approaches can be characterized as (Type A)photonic/optical modifications of the PV module or architecture, or(Type B) stand-alone radiative cooling systems. Existing PV-integratedsystems (Type A) have not demonstrated more than about 1° C. temperaturereduction compared to conventional glass covers. The existing Type Asystems may typically include undesirable modification of the panelmanufacturing process. The overall benefits of existing Type Aapproaches may be limited by the fact that the instantaneous solarheating rates (˜0.5 Suns) are significantly higher than radiativecooling rates (˜0.1 Suns). As disclosed herein, RAPT systems mayovercome the ratio of rates of instantaneous solar heating to radiativecooling and improve temperature stability. As disclosed herein, the RAPTsystem utilizes the area between the PV panel rows and extends theduration of cooling by advantageously applying stored nighttimeradiative/convective cooling.

Some existing stand-alone radiative cooling systems (Type B) may rely onthermally-emitting thin coatings on top of a solar-reflective substrate.Such Type II radiators may reflect sunlight at (or below) the thermalemitter leading to parasitically absorbed sunlight and limited coolingrates.

As shown in FIG. 2, unlike the stand-alone radiative cooling systems,some examples of the RAPT radiator disclosed herein include a ZnS-coatednanostructured polyethylene (nanoPE) layer to scatter sunlight near thetop of the cover 24. Examples of the radiative cooler disclosed hereinmay include a solar-scattering infrared-transparent nanostructured cover24 (ZnS-coated nanoPE) which blocks solar heat from reaching the thermalemitter (infrared radiating element) 22 (PDMS-coated mirrored Al).

In some examples, PDMS can be interchanged for a combination of otherpolymers such as TPX, polyimide, or rubber, as well as oxides such assilica and alumina, while maintaining the desired near-blackbody thermalemittance. The inverted structure of the RAPT radiator (top: scatterssunlight, bottom: emits IR) partially decouples regions that scattersunlight from regions that emit heat. The high refractive index of ZnSenhances the scattering properties of the nanoPE. The nanoPE may exhibitrelatively high total solar transmittance (˜40%) without ZnS enhancementbased on preliminary measurements as disclosed herein. Examples of theRAPT system disclosed herein compared to existing non-radiative systemsmay advantageously be dry (unlike evaporative cooling) and more passive(i.e. have negligible power consumption). Examples of the RAPT systemdisclosed herein may be integrated with other (i.e. non-RAPT) thermalmanagement systems.

Referring to FIG. 2, in some examples, the cover 24 has a low thermalconductivity coefficient and blocks incoming solar radiation withwavelengths <8 μm. The nanoparticle size and layer thickness of thecover are tuned to allow transmission in the infrared spectra between8-13 μm which is ideal for transmission of the waves through theatmosphere and into Space. The cover material can include BaF2, ZnS, andpolyethylene. TiO₂ and polyacrylonitrile (PAN) may also be included inthe cover 24.

In examples of the present disclosure, the radiators 22 can be tilted by10-15 degrees without loss of radiative power to enhance roll-off ofrainwater and particulates. In some examples, hydrophobic coatings maybe applied to promote self-cleaning.

FIG. 1 depicts a schematic view of an example of a Radiation-Assisted PVthermal management system 20 as disclosed herein. The ground-basedradiative cooler 46 provides continuous cooling of modules (solar panels12). The liquid reservoir 34 stores the excess nighttimeradiative/convective cooling energy and releases it during daytimeoperation. The liquid reservoir 34 may have thermal insulation disposedon at least portions thereof. The nanostructured cover and emitter areconnected to a shallow liquid reservoir 34 placed behind a solar array.A pump circulates the coolant to tubes 27 behind the active componentsof the solar panel 12. The coolant returns to the liquid reservoir 34and is cooled by the emitter (infrared radiating element) that passesthe heat into the atmosphere and through the atmosphere to Space. Theenergy required to operate the pump and emitter are provided by thesolar panel 12. With the radiative cooling system, the panel maintainsan operational temperature of about +7° C. to the ambient temperature of25° C. at times of peak solar exposure in which an uncooled panel willreach temperatures in excess of 50° C. Additionally, the systemmoderates the temperature decrease of the panels during nighttime. Thetemperature moderation provides at least two distinct benefits: first,it enables the field use of photovoltaic materials that are sensitive tothermal cycling; and second, the reduction of thermal cycling extendsthe service life of the photovoltaic which helps lower the LCOE byproviding a larger discount timeframe.

Referring to FIG. 1 and FIG. 2, in examples, a thermal management system20 for a photovoltaic (PV) power generator 10 may include an infraredradiating element 22, a solar-scattering cover 24 disposed on theinfrared radiating element 22; and a thermal storage sub-system 30 influid connection with a solar panel 12 via thermal interconnections 14.

In some examples, the solar-scattering cover 24 is to scatter sunlight11 diffusely (as depicted at reference numeral 39) or directionallytoward an underside 16 of the solar panel 12. The solar-scattering cover24 may be substantially transparent to infrared radiation to allow theinfrared radiating element 22 to emit infrared radiation through thesolar-scattering cover 24. In some examples, the solar-scattering cover24 may include a nanostructured, IR-transparent polymer 21. In someexamples, the nanostructured, IR-transparent polymer 21 may benanostructured polyethylene (nanoPE). In some examples, thenanostructured, IR-transparent polymer 21 may be nanostructuredpolyacrylonitrile (nanoPAN) 29. In some examples, the thermal managementsystem 20 further includes a dielectric material disposed on or embeddedin the nanostructured, IR-transparent polymer 21 to increase solarscattering of the solar-scattering cover 24 and to protect thenanostructured, IR-transparent polymer 21 from ultra-violet radiation.In some examples, the dielectric material is deposited on thenanostructured, IR-transparent polymer 21 by physical vapor depositionor by a solution-based process, or embedded into the nanostructured,IR-transparent polymer 21 by electrospinning. In some examples, thethermal storage sub-system 30 is to shift and distribute a peak solarheat load over a twenty-four hour time period; the thermal storagesub-system 30 is to store excess off-peak cooling for use during peakhours; the thermal storage sub-system 30 is to store natural convectionenergy; and the thermal storage sub-system 30 comprises a container 32to store a coolant. In some examples, the container 32 is located underthe infrared radiating element 22 or the container 32 is thermallyconnected to the infrared radiating element 22 via the thermalinterconnections 14. In some examples, the container 32 is connected tothe solar panel 12 with a circulating coolant line 28 or with heatpipes. In some examples, the heat pipes may be stationary, in otherexamples, the heat pipes may be to oscillate. In some examples, thethermal interconnections 14 include a circulating fluid loop or a heatpipe. In some examples, the thermal interconnections 14 are passive. Asused herein, “passive,” with respect to thermal interconnections meansthat the thermal interconnection is by natural circulation of air. Thenatural circulation of air may be directed by a structure (for example,a shroud or a vane), or the natural circulation may be undirected. Inundirected natural circulation, there is open air between the container32 and the infrared radiating element 22. In some examples, thedielectric material is selected from the group consisting of ZnS, ZnO,TiO2 and combinations thereof.

In some examples of the thermal management system 20, the solar panel 12may be a member 43 of an array 13 of tracking solar panels arranged inrows 15. The infrared radiating element 22 may be a solar-scatteringradiator 40 located between the rows 15 of the array 13 of trackingsolar panels. A radiating area of the solar-scattering radiator 40 maybe about equal to an area of the solar panel 12. The solar-scatteringradiator 40 may be to work in tandem with natural convection 44 from thearray 13 of tracking solar panels. The thermal storage sub-system 30 mayinclude a ground-based liquid reservoir 34. In some examples, thethermal management system 20 further includes a sun-facing surface 23defined on at least one member 43 of the array 13 of tracking solarpanels, a distal surface 25 defined on the at least one member 43 of thearray 13 of tracking solar panels opposite the sun-facing surface 23,and a heat exchanger 33 attached to the distal surface 25 of the atleast one member 43 of the array 13 of tracking solar panels. In someexamples, the heat exchanger 33 includes a serpentine tube 27, and theheat exchanger 33 is to obscure less than 20 percent of the distalsurface 25 of the solar panel 12 to which the heat exchanger 33 isattached. In some examples, the array 13 of tracking solar panelsincludes at least one bifacial solar panel 12. In some examples, thethermal interconnections 14 include flexible tubing to fluidly connectthe ground-based liquid reservoir 34 to the serpentine tube 27, whereinthe flexible tubing remains connected to the serpentine tube 27throughout a range of motion of a tracking solar panel 12 in the array13 of tracking solar panels to which the serpentine tube 27 is attached.

In some examples of the thermal management system 20, the ground-basedliquid reservoir 34 is covered by the solar-scattering radiator 40. Insome examples, the solar-scattering radiator 40 includes: a layer ofaluminum 31; a coating 45 disposed on the layer of aluminum 31, thecoating 45 to absorb or emit radiation having wavelengths ranging frommid-wavelength infrared to long-wavelength infrared; and a solarscattering cover overlaid on the coating 45, wherein the solarscattering cover is substantially transparent to infrared radiation 26to allow the solar-scattering radiator 40 to emit infrared radiation 26through the solar-scattering cover 24. In some examples, the layer ofaluminum 31 may have a mirror finish for specular reflection of thesunlight 11. In other examples, the layer of aluminum 31 may have arough surface that causes diffuse reflection of the sunlight 11. As usedherein, the reflection of light is categorized into two types ofreflection: specular reflection is defined as light reflected from asmooth surface at a definite angle, and diffuse reflection, which isproduced by rough surfaces that tend to reflect light in all directions.In some examples, the coating 45 is a selected from the group consistingof: polydimethylsiloxane (PDMS) or an other polymer; an inorganicmaterial; and combinations thereof. In some examples, the coating 45 ispolydimethylsiloxane (PDMS). In some examples, the solar-scatteringcover 24 includes a nanostructured, IR-transparent polymer 21. In someexamples, the nanostructured, IR-transparent polymer 21 isnanostructured polyethylene (nanoPE). In some examples, thenanostructured, IR-transparent polymer 21 is nanostructuredpolyacrylonitrile (nanoPAN) 29. In some examples, the thermal managementsystem 20 further includes a dielectric material disposed on or embeddedin the nanostructured, IR-transparent polymer 21 to increase solarscattering of the solar-scattering cover 24 and to protect thenanostructured, IR-transparent polymer 21 from ultra-violet radiation.In some examples, the dielectric material is deposited on thenanostructured, IR-transparent polymer 21 by physical vapor depositionor by a solution-based process, or embedded in to the nanostructured,IR-transparent polymer 21 by electrospinning. In some examples, thedielectric material is selected from the group consisting of ZnS, ZnO,TiO2 and combinations thereof.

It is to be understood that the terms “connect/connected/connection”and/or the like are broadly defined herein to encompass a variety ofdivergent connected arrangements and assembly techniques. Thesearrangements and techniques include, but are not limited to (1) thedirect communication between one component and another component with nointervening components therebetween; and (2) the communication of onecomponent and another component with one or more componentstherebetween, provided that the one component being “connected to” theother component is somehow in operative communication with the othercomponent (notwithstanding the presence of one or more additionalcomponents therebetween).

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range, as ifsuch value or sub-range were explicitly recited. For example, a range offrom about 8 μm to about 15 μm should be interpreted to include not onlythe explicitly recited limits of about 8 μm to about 15 μm, but also toinclude individual values, such as 9 μm, 11.8 μm, etc., and sub-ranges,such as from about 10 μm to about 12 μm, etc. Furthermore, when “about”or “˜” is utilized to describe a value, this is meant to encompass minorvariations (up to +/−10%) from the stated value.

While several examples have been described in detail, it is to beunderstood that the disclosed examples may be modified. Therefore, theforegoing description is to be considered non-limiting. No language inthis disclosure should be construed as indicating any unclaimed elementas essential to the practice of the examples.

What is claimed is:
 1. A thermal management system for a photovoltaic(PV) power generator, comprising: an infrared radiating element; asolar-scattering cover disposed on the infrared radiating element; and athermal storage sub-system in fluid connection with a solar panel viathermal interconnections; wherein: the solar-scattering cover is toscatter sunlight diffusely or directionally toward an underside of thesolar panel; and the solar-scattering cover is substantially transparentto infrared radiation to allow the infrared radiating element to emitinfrared radiation through the solar-scattering cover.
 2. The thermalmanagement system as defined in claim 1 wherein the solar-scatteringcover comprises a nanostructured, IR-transparent polymer.
 3. The thermalmanagement system as defined in claim 2 wherein the nanostructured,IR-transparent polymer is nanostructured polyethylene (nanoPE).
 4. Thethermal management system as defined in claim 2 wherein thenanostructured, IR-transparent polymer is nanostructuredpolyacrylonitrile (nanoPAN).
 5. The thermal management system as definedin claim 2, further comprising a dielectric material disposed on orembedded in the nanostructured, IR-transparent polymer to increase solarscattering of the solar-scattering cover and to protect thenanostructured, IR-transparent polymer from ultra-violet radiation,wherein the dielectric material is deposited on the nanostructured,IR-transparent polymer by physical vapor deposition or by asolution-based process, or embedded into the nanostructured,IR-transparent polymer by electrospinning, wherein the dielectricmaterial is selected from the group consisting of ZnS, ZnO, TiO₂ andcombinations thereof.
 6. A thermal management system for a photovoltaic(PV) power generator, comprising: an infrared radiating element; asolar-scattering cover disposed on the infrared radiating element; and athermal storage sub-system in fluid connection with a solar panel viathermal interconnections; wherein: the thermal storage sub-system is toshift and distribute a peak solar heat load over a twenty-four hour timeperiod; the thermal storage sub-system is to store excess off-peakcooling for use during peak hours; the thermal storage sub-system is tostore natural convection energy; and the thermal storage sub-systemcomprises a container to store a coolant.
 7. The thermal managementsystem as defined in claim 6 wherein the container is located under theinfrared radiating element or the container is thermally connected tothe infrared radiating element via the thermal interconnections.
 8. Thethermal management system as defined in claim 6 wherein the container isconnected to the solar panel with a circulating coolant line or withheat pipes, wherein the heat pipes are stationary or wherein the heatpipes are to oscillate.
 9. The thermal management system as defined inclaim 1 wherein the thermal interconnections comprise a circulatingfluid loop or a heat pipe.
 10. The thermal management system as definedin claim 1 wherein the thermal interconnections are passive.
 11. Athermal management system for a photovoltaic (PV) power generator,comprising: an infrared radiating element; a solar-scattering coverdisposed on the infrared radiating element; and a thermal storagesub-system in fluid connection with a solar panel via thermalinterconnections; wherein: the solar panel is a member of an array oftracking solar panels arranged in rows; the infrared radiating elementis a solar-scattering radiator located between the rows of the array oftracking solar panels; a radiating area of the solar-scattering radiatoris about equal to an area of the solar panel; the solar-scatteringradiator is to work in tandem with natural convection from the array oftracking solar panels; and the thermal storage sub-system includes aground-based liquid reservoir.
 12. The thermal management system asdefined in claim 11, further comprising: a sun-facing surface defined onat least one member of the array of tracking solar panels; a distalsurface defined on the at least one member of the array of trackingsolar panels opposite the sun-facing surface; and a heat exchangerattached to the distal surface of the at least one member of the arrayof tracking solar panels, wherein: the heat exchanger includes aserpentine tube; and the heat exchanger is to obscure less than 20percent of the distal surface of the solar panel to which the heatexchanger is attached.
 13. The thermal management system as defined inclaim 11 wherein the ground-based liquid reservoir is covered by thesolar-scattering radiator, wherein the solar-scattering radiatorincludes: a layer of mirrored aluminum; a coating disposed on the layerof mirrored aluminum, the coating to absorb or emit radiation havingwavelengths ranging from mid-wavelength infrared to long-wavelengthinfrared, wherein the coating is a selected from the group consistingof: polydimethylsiloxane (PDMS) or an other polymer; an inorganicmaterial; and combinations thereof; a solar scattering cover including ananostructured, IR-transparent polymer including nanostructuredpolyethylene (nanoPE) or nanostructured polyacrylonitrile (nanoPAN)overlaid on the coating, wherein the solar scattering cover issubstantially transparent to infrared radiation to allow thesolar-scattering radiator to emit infrared radiation through thesolar-scattering cover; and a dielectric material disposed on orembedded in the nanostructured, IR-transparent polymer to increase solarscattering of the solar-scattering cover and to protect thenanostructured, IR-transparent polymer from ultra-violet radiation,wherein the dielectric material is deposited on the nanostructured,IR-transparent polymer by physical vapor deposition or by asolution-based process, or embedded in to the nanostructured,IR-transparent polymer by electrospinning, and wherein the dielectricmaterial is selected from the group consisting of ZnS, ZnO, TiO₂ andcombinations thereof.